In this specification, where a document, act or item of knowledge is referred to or discussed, this reference or discussion is not an admission that the document, act or item of knowledge or any combination thereof was at the priority date part of common general knowledge, or known to be relevant to an attempt to solve any problem with which this specification is concerned.
Various different vehicle parking brake arrangements have been proposed in the past. A vehicle handbrake system (emergency or parking brake), for example, is supplementary to the vehicle's primary service hydraulic brake system. Systems of this sort conventionally feature a cable (usually adjustable for length) directly connected to the brake mechanism on one end and to some type of ratchet-engaged lever that can be actuated by the driver at the other end. On vehicles with automatic transmissions, selection by the driver of the ‘park’ position may be accompanied by activation of a parking pawl in the transmission.
Large vehicles are often fitted with power-operated or servo-assisted handbrake mechanisms. When releasing the handbrake, the same mechanism can also be used to provide assistance to the driver in disengaging the ratchet.
A more recently developed system is the electric parking brake, using an electric motor to operate the emergency brake cable, or a computer-controlled motor actuating the brake callipers.
Generally, such service or parking brake systems operate on the rear vehicle wheels (in the case of drum or disc brakes), or on the rear axle stubs (in the case of vehicles with disc brakes). However, there are disadvantages to the provision of such brake systems at or near the wheels or axle ends.
In demanding environments, such as industrial and off-road applications, such mechanisms are relatively exposed to the aggressive conditions below the vehicle (such as rocks, dust and other loose matter, and undulating terrain), and this can lead to significant maintenance and reliability problems.
Some alternative approaches have been proposed in the prior art.
U.S. Pat. No. 6,318,535 discloses a brake unit operating on the driving pinion of a vehicle differential transmission, with a mechanical configuration designed to avoid passing the braking torque to the differential transmission housing.
U.S. Pat. No. 5,673,776 discloses a parking brake system and a differential lock system, wherein operation of the brake also activates the differential lock. The two systems normally operate independently, but the invention ensures that when the vehicle is parked it cannot roll either in a straight line or (by virtue of the differential lock) in an arcuate path.
U.S. Pat. No. 5,687,611 discloses a parking brake for use with a power shift transmission of a forklift truck, employing a brake band wound around the brake drum of the output gear of a transmission input assembly, which can be tightened to effect the braking action.
Vehicle braking units are of course commercially available for a wide variety of applications. These include multiple disc brakes, such as through-shaft brakes, posi-torque winch brakes, pressure override brakes, and wheel mount brakes. Actuation of such units can be by a variety of means, including spring operation, hydraulic operation, cable operation, etc.
Aspects of the invention described below set out to provide a novel brake unit for use in potentially damaging physical environments.